Just came up with some data from the BENETEAU Lagoon 42 hybrid electric catamaran's user manual that makes it really clear about the power required and cruising distance achievable under battery ONLY power:
(highlighting is mine!)
5) BATTERY AUTONOMY
• Battery autonomy when operating under battery power alone is based on an
average motoring speed of 4.5 knots with less than 5 knots of wind
(after all, it is a
• Battery bank discharge from 100% to 80% will occur in approximately 2 hours.
• If the generator is intentionally prevented (manual cut-off) during its attempt to
automatically start and charge at the 80% level :
• Discharge from 80% to 60% will occur in approximately 1 hour.
• This means a total of 3 hours of range on the battery banks at 4.5 knots, knowing
that battery damage may begin to occur after the first 2 hours.
• At 60% charge level, the generator will again automatically start to protect the
batteries. If one tries to turn it off, it will remain running until the batteries are
charged. The only way to stop it is to manually cut the genset battery switch in the aft
starboard cabin to force it to stop.
•To maintain optimal battery capacity, it is advised not to navigate under
battery power alone for a distance of more than 9 miles
, which is considered
enough of a margin to get to a harbor and perform docking manoeuvers.
• Above the 13,5 mile range : risk of irreversible battery damage.
There we have it. Now you may ask...how many batteries does it take to go this 9 miles (in flat seas and if the wind isn't blowing and the waves aren't waving)...and you may ask how big they are and what they weigh:
The answer is TWELVE 8D's
...a mere 2500 amp hours
...a mere 2000 lbs
of batteries which you can't drain to the usual 50% capacity due to the heavy current draw.
I am NOT disparaging these boats since they come with a generator (11kw) that kicks in and powers you as long as the DIESEL holds out...It does go to show the folly of the proponents of "passive" recharge systems without a diesel. This boat in 2 hours at 1/2 hull speed in flat water uses 500 amp hours...1000 if you push it to 3 hours!! Your gonna need a fleet of CD's Catalinas just to keep the mother ship juiced up!!
Oh yeah...BTW...top speed with these electric engines running full out is 5.9 knots which is one of the ways they keep the POWER use down compared to the standard diesels which will drive the boat at 8 knots for several hundred miles compared to the electric model.